Japanese Patent Application Publication No. 2001-289028 (JP-A-2001-289028) describes an exhaust gas control apparatus for an engine, which is mounted in a diesel engine and which traps particulate matter (PM) in exhaust gas. The exhaust gas control apparatus includes a ceramic filter, a case that houses the filter, and a mat that is wrapped around the filter. With this structure, particulate matter is trapped in a wall of the filter when the exhaust gas is passing through the filter. As a result, the exhaust gas is purified.
In the engine in which the above-described exhaust gas control apparatus is mounted, as the amount of PM accumulated in the filter increases, the pressure of the exhaust gas increases. Accordingly, if a great amount of PM is accumulated in the filter, the filter may be moved with respect to the case in the downstream direction by the pressure of the exhaust gas. When the case and the filter come into contact with each other due to the movement of the filter with respect to the case, chipping or cracking may occur in the filter. Accordingly, the possibility of contact between the case and the filter should be minimized. However, there have not been proposed any technologies for minimizing the possibility of such contact. Not only in the above-described exhaust gas control apparatus but also in any exhaust gas control apparatuses including a purification structural body that is arranged in a housing and that purifies the exhaust gas, the purification structural body may be deformed due to contact between the housing and the purification structural body. Accordingly, the possibility of contact between the housing and the purification structural body should be minimized, as in the above-described exhaust gas control apparatus.